1. Field of the Invention
The invention relates to an improved landing nipple for use in a tubing string for receiving and housing a flow control device. More particularly, the landing nipple has a provision for closure of the flow control device in the event of seal failure in the nipple.
2. The Prior Art
It is common to provide landing nipples, for being made up in a tubing string, having a "dual line" control system for operating flow control devices landed in the nipple. Such landing nipples provide for the transmission of pressure fluid to the nipple, with the control pressure fluid generally being used to open the flow control device to allow passage of well fluids to the surface.
Modern flow control devices sometimes have "balance" pressure chambers for off-setting the hydrostatic pressure generated by the column of fluid in the control line. Thus, the "dual line" provides essentially equal hydrostatic pressure to assist in closing the flow control device.
In order to isolate the control and balance pressure zones, of a dual line landing nipple, from tubing bore pressure, seals are arranged on each side of the pressure zone. It is possible in such arrangements for tubing bore pressure to get around such seals and enter the control pressure line. If the tubing bore pressure is greater than the hydrostatic pressure in the balance line plus the flow of the closing spring, the flow control device can "fail" in the bore-open position. Thus, a potentially dangerous situation has been created.
A dual line landing nipple for receiving a remote controlled tubing safety valve is illustrated on page 4001 of the Composite Catalog of Oil Field Equipment and Services (1974-75). While the landing nipple illustrated therein is for use with wire line equipment, those used for pump down services are virtually identical in operation. Pump down services for well production and completion is discussed in the Composite Catalog, supra, commencing on page 4070.
The drawings in this application illustrate use of the nipple of this invention with pump down flow control devices. Such pump down equipment is referred to as "through the flow line" or TFL equipment. However, the invention is applicable to both TFL and wire-line equipment.